As a complete newbie myself I will off my start advice:
0. Update the game to the latest version if it isn't already. I also start with the default AI/level constraints.
1. I don't believe the slave labour and rigid traits are worthwhile:
a) Slave labour boosts labour, but initially you are (read I was) resource starved rather than labour starved, so the bonus labour would go to waste.
b) Rigid prevents you using the civil policy 'academics' (or similar off the top of my head), which gives a 10% boost to the production of metals, electronics and advanced parts at the cost of generating 50% less labour.
So that said, the traits that I chose:
'Green thumbs' so I could start with level 2 biology. The reason I chose to start with this is because it allows me to use biology as my hunch/guess technology to unlock all of chemistry, nanotechnology, computers and sociology, instead of having to guess off of other things first and potentially duplicating research. This also allows me to chose:
'Higher metabolic rate' so I consume double the food, but my population grows quicker. This results in starting colonies growing quicker, and I already have extra food from the other trait.
'2nd planet' (not the name but the effect), this allows me to start with 2 build queues.
'indebted' This penalises using the galactic bank in the first 20 minutes of the game. To get around this, I use the civil act of stockpiling so my planets need to be close to full before anything goes to the bank. I then redesign the starting hauler to scale 1, up the engine to maximum, cut the fuel cell size to enable 1-2 minutes of flight and build these on the second planet (after getting rid of 1 advanced parts factory to build another electronics factory on the second planet (15/15)).
'random technology to tech level 3' in the hopes of getting sociology so that my starting cities are bigger, however beam weapons, shields, sensors, mega construction are also all good. If you do get sociology, you will want to research another level of biology very quickly or you will start to starve.
'Eusocial' the one that gets rid of the requirement of goods and luxuries - I'm on the fence with this one, I'm unsure whether it counts as a bonus or a malus of the top of my head also.
I also adjust some of the starting ships:
Colony ship: increase size to 17.66, put 5 coloniser modules size <0.75 (actual size less than this doesn't matter), life support to match, engine to max, drop other components to minimum to maintain power/control etc. I also decrease the fuel size so it has about 1-2 minutes of fuel, this is a short lived blueprint.
Scout: Swap engine for 2 maxed bussard ramjet, then remove all other components. Can decrease scale too.
Dry dock: Remove bulkheads, increase number of construction bays, reduce cargo bays, reduce scale to 10.
Hauler: As described above. (reduce scale to 1, upscale the engine, reduce fuel storage, potentially increase cargo bay)
That's the pre-game sorted.
Start of game. Ideally you start the game in a homeworld system with a total of 4 planets.
Civil Acts: Academics on permanently and stockpiling on for the first 20 minutes. Use the focus/mandates as and when required which will usually be significantly later. Set 'park in orbit' on for new ships and I like to set the governor to balanced as it will by default build a planetary cannon, science labs and a 'balanced' mix of metal/electronics/advanced parts, a shipyard first to speed construction of all the other colony buildings and it won't get rid of the starting farm that this size coloniser gives your colonies. Your colonies will also start with a metal mining facility.
Research: Start with 1 of metallurgy and 1 of general science.
Homeworld: Build a shipyard, 2 science labs and a drydock. Once the drydock is complete, remove a shipyard and replace with a science lab, then remove the other and replace with yet another science lab. Set the local governor to renovate only. This way you won't have to worry about updating all the mines/factories/labs on the planet every time a tech level increases.
Drydock: Once complete, build enough of these first colony ships to colonise the homeworld system. After them put a batch (ctrl click) of 150 scouts or galaxy size, then upto 20 bombers.
Colony: Remove an advanced parts factory and replace with an electronics factory. build 4-5 haulers. Build more haulers gradually over the space of the next 10 minutes (perhaps 1 per minute). Set the local governor to renovate only.
Research: Once you have researched 1 in metallurgy and 1 in general science, I research up to 3 in engineering (+2) and 4 in ship construction (+3). This has a few benefits:
1. Shipyards are bigger on fledgling worlds.
2. Opens up the light hull - an extra subsystem slot and I think it is meant to be cheaper.
3. Opens up the external mount - as a modifier to a subsystem you can make subsystems able to be mounted externally so they only take up 1 space on the ship, this is useful for size 4 components. The downside is these components will be the first damaged when the ship takes damage. Not much of a disadvantage at this point!
4. Improves life support and several other components.
With these researched you will want to research metallurgy and general science alternating again up to about 4 each. Notice we aren't researching economics - we aren't using the space ports so much due to stockpiling and haulers moving the goods within the local system and this means the penalty of 'indebted' is avoided and we can delay researching economics until later - this has the benefit of allowing us to improve the research in the aforementioned areas without taking too big a hit to our economy.
You will now want to design a colony ship at scale 15 with 2 size 4 coloniser modules mounted externally and suitable life support and enough power/control/engines to allow a large amount of thrust (high acceleration) with enough fuel for maybe 5-10 minutes. This will make colony ships with 8 buildings: Which includes a metal mine, an electronics factory and an advanced parts factory - so your next colonies that are out of the home system will be able to grow at least a little without the need for a space port. Good job as your galactic bank will be empty due to 'indebted' and stockpiling.
As the first system to colonise, try to find the system that has a red star which is listed as being vulnerable to detonation due to elements at its core - by the time this would be a liability you should be able to defend it and have already gained an advantage from this system. The reason for trying to claim this system (which is hopefully close - I have started games with it right next door to my home system!) is that the planets in this system are particularly large, some in excess of 30 slots and there are usually 5 planets (your scouts will have long since told you how many colony ships to build). This will probably end up being the manufacturing centre for your empire when it is built up, aim to come back here when they finish completing colony buildings and build at least 1 dry dock per planet, or 2-3 around 1 or 2 planets and a fleet of 20-50 haulers to take resources from the other planets to the planets that have dry docks. Try to build at least 1 dry dock per completed system and a supporting fleet of haulers.
When your first new version of the colony ship is built, send ~7 bombers with this first colony ship, you should at this point be 1st in military, economics and research against the default AI, and perhaps 2nd/3rd in colonies depending on the number of planets in your home system. When you have about 4 in metallurgy and 4 in research, research up to 5 in energy sciences (+4) and 5 in propulsion (+4). Keep an eye on the timer - these will improve your engines, and open up the option for fusion power plants and ion thrusters which use less fuel at the cost of the fusion power plants being more expensive - ion thrusters are definitely worth it as your ships can be made cheaper with the same lifespan. When it reaches 20 minutes, if you aren't about to immediately finish researching something, quickly queue up at the start of the research queue about 4 levels of economics, this will level off your economics to about where it would be with 1 metal, 1 research and 1 economics alternating. Ideally you will be looking at having maybe 5-6 metallurgy, 5-6 general research and be about to start economics at the 20 minute mark, with some side research as mentioned earlier in the propulsion/ship construction/engineering/energy fields.
Once I hit 6 metal and 6 general research, I start performing the hunches/guesses in biology (starting with the one that is most unlocked already - typically one will start about one third done) and hope to unlock the 4 locked technologies off the first 4 links - if you do then you can cancel the 5th link as this will only give you a tech level in material sciences which isn't needed right now. Once you have unlocked these, research a few levels of sociology and biology to match to prevent starving, as these will increase the size of your cities which increases the size of the population level, which means either fewer cities (more factories sooner) or higher population level (multiplies the effectiveness of the factories). The next step is to research up to 8 metallurgy (+2) and 6 computers (+6 - which will actually take no time at all) and 6 economics (+~2). Then you may want to put a couple of levels into general science and go for 10 metallurgy (+2), 8 computers (+2) and 6 nanotechnology (+6). These each unlock a new economic module for your ships which can replace or at least augment production facilities on the planets surface.
With the electronic fabrication subsystem you can design a space station (I go for size 50 by this stage) that will take metal from the planets surface, and make it into electronics, then using the export dock send it to the galactic bank which by now should be filling up with metals. You will want to build quite a few of these so that your electronics (which I find to be the component in shortest supply) will start building up stockpiles. During this time you should be continuing to produce colony ships from the home world system and expand to the nearest non-remnant system that isn't already fully colonised, sending a few bombers to each new system to be colonised in advance. At this point you may find yourself slipping to maybe 2 or even 3 military but in position number 1 for the other 3. If you find the other empires are starting to get demanding and threatening war, you may want to see what their biggest warship is, and up scale the capital ship to a scale about 100 higher and start building these at all free dry docks. This should put you to number 1 in all fields and make the enemy empires less aggressive in demands to you, if they offer research for resources, I tend to take it, likewise if I feel they are giving lots of 1 particular resource for relatively little in return.
There will come a point where the enemy empires will attempt to make a big land grab, if you can anticipate this moment and push yourself to get a huge land grab before them (dry docks everywhere building 5 colony ships each using the sector menu and all dry docks, then with shift held double click the colony ship), then go around and mark all systems (at this point your starter colonies may be able to survive entering the smaller remnant systems and be able to build a shipyard and a planetary cannon) for auto-colonise and beat them all to the systems - this should put maybe half to two thirds of the galaxy under your control. You will have ideally wanted to have unlocked all technology fields (except maybe stealth, I haven't used that one) and be ready to use 'automate research' to grab about 7 or 8 levels in all the unleveled fields so that your planetary cannons will be big and everything about your ships is more capable than the enemies.
At this point you will need to test and see what works for you as you will now be at the point where you will have to take systems from other empires by force. I like using scale 300+ ships with large shields/chargers so that the enemy cannot easily penetrate, with the weapon of choice being the reverse inductor so that I can kill a lot of ships with 1 shot - if they require power. A second weapon is handy for killing stations - apparently a repulsor can be a good idea to just push them out of the system - they have no engines to come back.